The present invention relates generally to an imaging module and an imaging reader for, and a method of, imaging targets to be electro-optically read by image capture over a range of working distances, and, more particularly, to expeditiously setting one or more imaging parameters, such as exposure and/or gain values, of an imager based on a previous setting of exposure and/or gain values determined for a default imager.
Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbol targets, and/or non-symbol targets, such as documents. A handheld imaging reader includes a housing having a handle held by an operator, and an imaging module, also known as a scan engine, supported by the housing and aimed by the operator at a target during reading. The imaging module includes an imaging assembly having a solid-state imager or imaging sensor with an imaging array of photocells or light sensors, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged, and for projecting the return light onto the array to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electronic signals corresponding to a one- or two-dimensional array of pixel data over the imaging field of view.
In some applications, for example, in warehouses, it is sometimes necessary for the same reader to read not only far-out targets, e.g., on products located on high overhead shelves, which are located at a far-out range of working distances on the order of thirty to fifty feet away from the reader, but also close-in targets, e.g., on products located at floor level or close to the operator, which are located at a close-in range of working distances on the order of less than two feet away from the reader. The reader may capture the return light from the far-out targets by employing a far-out imager having a relatively narrow field of view, and may capture the return light from the close-in targets by employing a close-in imager having a relatively wide field of view.
However, the use of more than one imager presents a challenge to reader performance. For optimum reader performance, each target must be read by the correct imager, and the correct imager should be set with one or more optimum imaging parameters, such as exposure values and/or gain values. These values are typically different for each imager, and vary, among other things, as a function of the working distance and the brightness of the captured image. Increasing the exposure and/or the gain values of each imager will increase the captured image brightness of the image of the target, and vice versa.
In order to set one or more optimum imaging parameters, it is known for a default one of the imagers to capture an entire image from the target in a frame, to analyze the brightness of the entire image, to change the imaging parameters based on the analysis of the brightness of the entire image, to capture another entire image from the target in another frame, and to repeat all the steps of this process for as long, and for as many times, and for as many frames, as it takes until the brightness of the entire image is within an acceptable level to enable the target to be successfully read by the default imager. If the target is not successfully read by the default imager, then it is known for the reader to switch to the other imager, and to again repeat all the steps of this process for as long, and for as many times, and for as many frames, as it takes until the brightness of the entire image is within an acceptable level to enable the target to be successfully read by the other imager. An automatic exposure controller (AEC) is typically used to control each imager's exposure, and an automatic gain controller (AGC) is typically used to control each imager's gain. A typical known strategy is to use exposure priority, in which the exposure is increased first until a maximum exposure time or threshold (typically around 4-8 ms in order to reduce hand jitter motion effects for a handheld reader) is reached. If the image brightness is still too low, then the gain is increased. This strategy maximizes the signal-to-noise ratio (SNR) of each imager, because the gain is only increased when necessary.
Although generally satisfactory for its intended purpose, this known multi-step process is very slow and inefficient in practice, especially when more than one imager is involved, and when the entire known process has to be repeated for each additional imager. Reader performance can be deemed sluggish, and is unacceptable in many applications.
Accordingly, there is a need to expeditiously set a default imager with one or more optimum imaging parameters, and to expeditiously set one or more optimum imaging parameters for another imager based on the imaging parameters that were previously set for the default imager, in order to more rapidly, efficiently, reliably, and successfully read both far-out targets and close-in targets with the same reader.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.